Confirmation of extended annihilation-line emission in 2005 January 20 flare: Earth

occultation.

Day Night

Evidence for hard particle spectrum in the 01/20/05 flare

Hard (pion?) Component

Spectrum dominated by bremsstrahlung (dots), 511 keV and n-capture (2223 keV lines and hard component. Narrow lines (solid) not clearly detected also suggesting hard spectrum.

Calculated gamma-ray spectra vs flare-accelerated particle power-law index. Nuclear continuum masks narrow lines for hard spectra.

Spectrum after hard component subtracted

Extended 511 keV flux comes from high-energy solar photons interacting in the spacecraft. Are these from solar pion radiation? High-energy appears to contain

particles >07:15 and possibly neutrons >06:55.

Counts >20 MeV shows early peak coincident with sharp peak at 511 keV (likely to be high-energy solar photons causing instrumental line). Later peaks suggest neutron detection and strong particle emission (lat > 30o). Abrupt drop in rate at Earth occultation consistent with high-energy solar photons.

511 keV line is broad early in flare and is dominated by the delayed beta-decay produced solar annihilation line. Late in the flare line is narrower, consistent with instrumental origin associated with high-

energy solar photon impact on the spacecraft.

Spectra from three RHESSI flares revealing differing amounts of pion radiation inferred from 9-16 MeV emission. Coronas confirms pion emission in the October 28 and January 20 flares. No evidence for pion emission in November 2 flare

1/20/2005

10/28/2003

11/02/2003